Liquid fuel atomizer located upstream of a flame stabilizing baffle



Nov. 3 J. REID ET AL LIQUID FUEL. ATOMIZER LOCATED UPSTREAM OF A FLAMESTABILIZING BAFFLE Filed Aug. 23, 1949 FUEL SUPPLY ELECTRODE FIG. I

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I! III FUEL asgg-jflv p- L Q t m m m 4 v M n f. m 0.0 AMIA F D u g In W,M #8 D J Patented Nov. 3, 1 953 LIQUID FUELATOMIZER LOCATED UP- STREAM!OF A; FLAME STABILIZING JlohnzReid -Elstead and Allan-G. Earl,Camberley, Englandpassignors; to Power Jets (Research and Development)Limited, London; England,

aIBritish. company ApplioationAugust 2 3, 1949; Serial 'No. 111,914(llairm-pribrityaI application Great Britain September 2, 1948- 7Claims. (01. (so-39.72)

This invention srelats m aaimpi tsd combus i on. armra'tus fer.burninglidnid fuelg and. providesa method and. apparatus. whereby a.high.

which ,cdmbustipn.haa to jbel started. and. supported thereafter in anair .flo v-oh-fiame. extinguishing velocity, a. combustion stabilising.baifle' means. adjacent. which-a combustion stabilizingzoneisformed.iriQWhichQthevelocitjz issufiiciently low. for,a.stable.'flarfie.to. burn once started-not.- withstanding' a iflame.,.exltinguishing mean. over.- all velocity of fioil'zpastsaid zone. andoneor more.

fuel, atomisers; in; saidfducting atilea'st; one of which. is.looated'relativ'e .tocombustion. stabilising.

means so. thatv a. portion; of'th'e'i. fuellf airv mixture. 7

will" pass to the combustion stabilising'zlone/for the stable flame, theor each fuel atomiser" c011 sisting of-aw lieuidfuelsupply jei; onj'etsfor directing astr-eam-(sJ- oil-fuel under pressure againsd aresisting.- medium spaced: awayfronr theijettsi at a distance.sufiiciently small in -relation to ambient -conditions. that thestreamof fu'el remains. compactand. continuesso until-it: strikes the. mediumvWhereit, spreadssubstantially. radially at,,high ..speed;inl a film, orsheet frbm the area of. impact, intothe. main. air stream; 7

Thefunction t. thel-baflie to; create in the.- stream of air-fuelmixture a turbillentszone-in. Whichthe mixturehaaa.low. veloolty(axiallyof the duct). sethat'ihmziybe easilyignitedtoprw vide a pilotflame. This pilot flame. initiates. combustion and promotes: great.stability of. combustion. serving; tor heat the remaining. portion,

of' the mixture by conduction and causing;- the continuous. (and..self..propagating). combustion of this remainingportion of. thefuel-Iain mix-- ture.

form an anvil which the jet of fuel strikesgagainst and thenspreadsoutwardsat high: speed; 7

The resistingmedium-may also be a jetof liqiuid which will supportcombustion-ora-jet'of gas:

In-.a. modified form the. apparatus provides stream end of the bafile.

Theresisting medium may be a, solid surface j placed-a short distanceaway'fromthe fuel'jet to These fluids issue from assecondarigjfi i012*."

posed to the fuel suppligiet. Ingthe,former.case; the liquid isdesirably a second jet of fuel. In

2 the latter-case it may be asuitable gas or jet of air: or othersuitable. mixtures of gases not necessarily combustible.

In the particular application of the novel combustion apparatus.according to the present invention, ea. aram-jetusystem as. will be.hereinafter. described and; comprising atomisers having secondary jetsit is essential that a jet of gas or mixturezof gases iszusectas-theresisting medium,

The jet acting asthezresistingmedium and the fuel supply: jetarearran'ged'j so that the fuel and fluid streams strike one; anotherand. thus. create initially: a substantially." fiat. sheet ofcombustiblefluid; mixture spreading awayfrom the impact point. The main air supplyis most conveniently furnished. by arranging: the atomisers. in. a ductwhereby this. air and the. combustible atomised mixture are: thoroughlymixed before combustion. The atomised, fuel: isbest distributed if themain air stream is supplied. to the combustion zone by the; duct andifthe axis ofthe fuel jet lies parallel touthe. axis of the cluctand theplane of the anvil which the jet strikes lies transversely of the duct.Also with the. opposed jetatomiser 'the' best results:- areobtained ifthe axes of both fuel supply jet(s) and secondary jetts) are in line andparallel to the axisof: theductawhereby the atomised: fuel mixture is.thoroughly dispersed across: the main air stream flowing. through. theduct.

The atomis'ers are so located relative to the bafllethat a: portionofthe fuel-air mixture will be sucked into the turbulent zone at thedown- In general it has been found the atomi's'ers' should not befurther downstreamthan the downstream end of the bafiie; In particularcircumstances however the turbulentzoneis formedslightly downstream ofthe bafile and theat'omisers may then be placed downstream of theba'fllebut upstreamof the commencement" of the turbulent zone.

The bafiie dimensions must--not be so large-in relation-to-theduct astocause big pressure losses in the duct 01" the-efiiciencyof the systemwill be reduced. The pressureloss maybe expressed in thefollowinggeneral'terms; At air velocities at Mach number-0.2 upstream"of the baffle the ratio of air pressures. downstream andupstreamofthe-baflle: shouldribe' of the order of 0:96;

A convenientzform-bfi baffle is a hollow-cone located centrally intheduct. with its vertex upstream, The blockage:ratioof'such.a baflle, thatistheratio of the'maximum cross-sectionalarea of thebaflle to, the area. of the duct should beabout 45% and the ratio upstream area m to thedownstream area a2 that is cone area ratio should be about 25:1. Thebafiie may be arranged to carry one or more fuel supply jets at thevertex while the anvil or secondary jet is carried on a separatestreamlined support. In another arrangement of the combustion apparatusthe baffle may comprise a hollow truncated cone with its vertex pointingupstream, and with one atomiser located with its jet axis in line or itsjet axes parallel with the cone axis and upstream thereof. Several moreatomisers may be distributed around the exterior of the cone andupstream of its downstream end. The atomiser upstream of the cone servesas a pilot atomiser as a proportion of the fuel-air mixture passing downstream therefrom fiows directly into the turbu lent zone caused by theconical baffle via the hole at its vertex and round the downstream edgeof the cone while the atomiser disposed around the cone furnishes themain fuel supply. Part of the main fuel-air mixture also passes over thedownstream edge of the cone into the pilot flame region and theremainder is heated by conduction from the pilot flame and burns furtherdownstream.

The most convenient means for igniting the fuel-air mixture is toinstall an insulated electrode in the apparatus such that it projectsinto the pilot flame or turbulent zone. When an electrical current isapplied a spark will pass to the baffle and start the combustion. Whenthe baiile is a hollow cone the electrode is best located such that thespark passes to the interior of the cone. Ignition may also be initiatedby a thermite charge itself ignited by an electrically heated wire.

One particular mode of employment of the combustion apparatus accordingto the invention will not be described, viz: its application to aram-jet combustion system as illustrated in the appended drawings inwhich:

Figure 1 is a sectional side view of a single ram-jet combustion systemhaving a single atomizer,

Figure 2 is a sectional view to a smaller scale of a ram-jet combustionsystem having a plurality of atomisers and Figure 3 is a cross sectionat IIIIII of Figure 2 showing the disposition of the atomisers.

Figure 4 is an enlarged view of an opposed jet atomiser, such as isshown in Figures 2 and 3.

In Figure l, l is a cylindrical duct for conveying the main air supplyand which on the downstream side of the atomisation zone constitutes acombustion chamber and tail pipe generally indicated at 1. In theatomisation zone the system is constituted by an atomiser having a fuelsupply jet 2 fed through a fuel supply pipe 4 and an anvil 3 carried bya faired or streamlined support 8. A baffle member 5 in the form of ahollow truncated circular cone closed at its smaller end is also carriedby the support 8 and is located centrally in the duct, vertex upstream.The downstream end of the cone is approximately two thirds the diameterof the duct and the vertex angle of the cone about 30. The bafflecarries at the upstream end a fuel supply jet 2 with its axis parallelto the duct axis. Immediately upstream is the co-operating anvil member3 placed centrally in the duct with its surface lying transversely ofthe duct so that fuel striking it will spread radially outward and bedispersed over the whole cross section of the duct into the mainair-stream. The angle at which the main air supply flowing over theanvil 3 4 strikes the fuel flowing radially from the flat surface of theanvil is preferably The system functions as follows. The baflie createsa turbulent zone in the mixtures within and. immediately downstream ofthe baffle in which zone the mixture has a low velocity axially of theduct. This portion is ignited by a spark passing from electrode 6 tobaflle 5 and combustion then becomes self-propagating, a portion ofmixture being constantly drawn into the turbulent zone where it ignitesand acts as a pilot flame and also heats the other portion of themixture passing down the duct.

In Figure 2 each of the atomisers consists of a fuel supply jet 9 and asecondary jet in axially opposed thereto, both jets having their axesparallel to the duct axis. Five atomisers are provided and the bafiie isin the form of a hollow truncated cone ll of similar dimensions as thatin Figure 1. It is located centrally in the duct vertex upstream and iscarried on streamlined supports. One atomiser is located upstream of andwith its jets axially in line with the cone. The remaining four are, asshown also in Figure 3, disposed symmetrically about the baffleintermediate its upstream and downstream limits. Ignition is carried outas in the apparatus of Figure 1. In this modified system fuel-airmixture from the single atomiser upstream of the cone is carried intothe cone via the entry hole and ignited there together with a portion ofthe main charge furnished by the other four atomisers which is sucked inby eddies at the downstream end of the cone. The mixture within the coneis ignited and combustion proceeds as in the apparatus of Figure 1.

Figure 4 shows the general arrangement of an opposed jet atomiser.Dimensions X and Y" are critical and the following dimensions should beconsistent with strength. The shape should be such that as low aresistance as possible is presented to the main air-stream.

A combustion system constructed substantially in accordance with Figures2, 3 and 4 incorporating a diffusion zone and having the followingdimensions:

Duct diameter at A inches 6 Cone baflle taper degrees 30 Cone upstreamdiameter in 0.75 Cone downstream diameter in 4.00 Jet dimension X in0.15 Jets dimensions Y mm.. 2

has given the following results using petrol issuing from an upstreamjet as the fuel and an air blast issuing from the downstream secondaryjet as the resisting medium to break up and disperse the fuel.

(1) A rich mixture flame extinction limit of air-fuel ratio 10:1 at mainair velocities up to 250 ft. per sec.

(2) A weak mixture flame extinction limit of an air-fuel ratio 150:1 atmain air velocities up to 400 ft. per sec.

(3) Combustion efficiencies of 90 to at chemically correct mixturestrengths for complete combustion up to velocities of 250 ft. per sec.using a combustion chamber tail pipe of length 4'6".

The following additional data is applicable to result (1) similar databeing obtainable for the other two results:

Fuel fiow=2000 lb/hr. Main air supply=5.7 lb/sec.

The above results illustrate the advantages obtained by the new systemin a particular application, viz: combustion stability over a wide rangeof main air velocities and mixture strengths coupled with a highcombustion efficiency. Furthermore, in the special application to aramjet combustion system these advantages are maintained over a widerange of air densities and fuel flows as the atomisation of the fuel isnot dependent on these factors but on the excess pressure of theauxiliary air supply or the fuel supply above the combustion chamberpressure.

We claim:

1. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a fuel atomizingsystem in the duct, said system comprising at least one liquid fuelinjector directed along the duct and means to provide a resisting mediumfacing and close to said injector so that fuel issuing from the injectoris caused to spread out across and mix with the stream, flamestabilizing bafile means in the duct adjacent to, downstream of andaligned with the atomizing system, said baflle means defining astabilized combustion zone, and an igniter within said zone.

2. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a fuel atomizercoaxially located within said duct, said atomizer consisting of a liquidfuel injector directed axially of the duct and an anvil facing and closeto said injector, upon which said fuel impinges to spread out across andmix with the stream, a flame stabilizing bafile co-axially located inthe duct adjacent to but downstream of the atomizer, said baffledefining a stabilized combustion zone, and an igniter within said zone.

3. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a fuel atomizercoaxially located within said duct, said atomizer consisting of a liquidfuel injector directed axially of the duct and an anvil having a surfaceextending transversely of the duct and facing and close to saidinjector, upon which surface said fuel impinges to spread out across andmix with the stream, a flame stabilizing baflle defining afrusto-conical interior cavity, said baflle being co-axially located inthe duct adjacent to but downstream of the atomizer, said cavity of thebaffle defining a stabilized combustion zone, and an igniter within saidzone.

4. Combustion apparatus for burning fuel in a fast-moving gas streamincluding a duct for carrying said stream, a plurality of fuel atomizerssymmetrically disposed in the duct, each said atomizer consisting of aliquid fuel injector directed along the duct and means to provide aresisting medium facing and close to each injector, so that fuel issuingfrom each injector is caused to spread out across and mix with thestream, flame stabilizing baflle means in the duct 6 symmetricallydisposed with respect to the atomizers adjacent to but downstream of theatomizers, said baflie means defining a stabilized combustion zone, andan igniter within said zone.

5. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a fuel atomizingsystem symmetrically disposed in the duct, said system comprising atleast one liquid fuel injector directed along the duct and a furtherfluid injector facing and close to and alined with said fuel injector,whereby said fuel and fluid impinge upon each other to spread out acrossand mix with the stream; flame stabilizing baflle means in the ductaligned with, adjacent to and downstream of the atomizing system, saidbaflie means defining a stabilized combustion zone, and an igniterwithin said zone.

6. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a fuel atomizerco-axially located within said duct, said atomizer consisting of aliquid fuel injector directed along the duct and a further fluidinjector facing and close to and alined with said fuel injector wherebysaid fuel and fluid impinge upon each other to spread out across and.mix with the stream, a flame stabilizing bafile co-axiallY located inthe duct downstream of but adjacent to the atomizer, said baffledefining a stabilized combustion zone, and an igniter within said zone.

7. Combustion apparatus for burning liquid fuel in a fast-moving gasstream including a duct for carrying said stream, a frusto-conicaltubular member coaxially located within the duct, said member beingdivergent in the downstream direction, a fuel atomizer located at theupstream end of said member, a plurality of further fuel atomizerssymmetrically spaced around the outside of said tubular member, eachsaid atomizer consisting of a liquid fuel injector directed along theduct and means to provide a resisting medium facing and close to saidinjector, so that the fuel is caused to spread out across and mix withthe stream, and an igniter within said tubular member towards thedownstream end thereof.

JOHN REID. ALLAN G. EARL.

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